In the 3rd Generation Partnership Project (3GPP), a W-CDMA system has been standardized as a 3rd generation cellular mobile communication system and services have been launched. HSDPA having a higher communication speed has been also standardized, and services have been launched.
Meanwhile, in the 3GPP, an evolved 3rd radio access (Evolved Universal Terrestrial Radio Access: hereinafter, referred to as “EUTRA”) technology has been standardized, and services have been launched. As a downlink communication method of the EUTRA, an orthogonal frequency division multiplexing (OFDM) scheme which has high resistance to multipath interference and is appropriate for high-speed transmission has been employed. As an uplink communication method, there has been employed a discrete Fourier transform (DFT)-spread OFDM scheme of single carrier-frequency division multiple access (SC-FDMA) that can reduce the peak-to-average power ratio (PAPR) of a transmission signal in consideration of cost and power consumption of mobile station apparatuses.
In the 3GPP, discussion on the Advanced-EUTRA which is further evolution of the EUTRA technology has been started. In the Advanced-EUTRA, it is assumed that communication is performed at a maximum transmission rate of 1 Gbps or more in a downlink and at a transmission rate of 500 Mbps or more in an uplink by using a band up to a maximum bandwidth of 100 MHz in the uplink and the downlink.
In the Advanced-EUTRA, it is considered that a maximum bandwidth of 100 MHz is achieved by binding a plurality of bands compatible with the EUTRA such that a mobile station apparatus of the EUTRA can be accommodated. In the Advanced-EUTRA, one band of 20 MHz or less in the EUTRA is called a component carrier (CC). The component carrier is also called a cell. The binding of the bands of 20 MHz or less is called carrier aggregation (CA) (NPL 1).
In the Advanced-EUTRA, it has been examined that the carrier aggregation of a macrocell and a small cell present in the coverage of the macrocell is performed within a frequency or between frequencies. A case where the small cell is present in the coverage of the macrocell may include a case where frequencies are different. NPL 2 discloses that in the communication between the base station apparatus and the mobile station apparatus at the time of the carrier aggregation of the macrocell and the small cell, the macrocell transmits control information (control-plane information) and the small cell transmits user information (user-plane information). The carrier aggregation of the macrocell and the small cell disclosed in NPL 2 is called dual connect (or dual connectivity).
In the dual connect, it is considered that information on the same radio bearer (RB) is transmitted to the mobile station apparatus from the base station apparatus as the macrocell and the base station apparatus as the small cell and the information on the same radio bearer (RB) is transmitted to the base station apparatus as the macrocell and the base station apparatus as the small cell from the mobile station apparatus. Control performed such that the base station apparatus and the mobile station apparatus transmit and receive the information on the same radio bearer through different base station apparatuses is called bearer split.